Corbin's Treehouse - Corbin Dunn, Santa Cruz, CA
Plug Bug

Archive for the 'Machining' Category

New Corbin UniBar (unicycle handlebar)

I made a new handlebar for my geared KH26. I was using the KH T-bar, but it feels really flexy and it feels like the seat will eventually break from the pressure I put on it. I had already made a slightly longer and slightly wider T for it out of CroMo steel, but it was just as light as the aluminum original.

Here’s the new bar, completed and installed:


New bar, 352 grams:


Old bar plus the seat strengthen plate (not needed with my design):


So, 150 gram savings in weight by using CroMoly steel. And it is a lot less flexy!

Building process:

1. Fabricated a lug:


2. Brazed it onto the seat tube attachment:


3. Not shown, brazed on the back tab for the bolt/cincher

4. Cut a T, made a fish mouth in the end, and brazed on the top:


5. Inserted the 22.2 tubing into the “lug” and brazed it together. The lug adds strength; I’ve broken handlebars at that location.

Making the LED Cyr Wheel / Roue Cyr – version 1

Here are my rough notes about making my LED cyr wheel (version 1). A Video can be seen here.

Edit: 12/28/2013: Here are some problems I am having with this  LED Cyr Wheel v1

I used a new technique for bending wheels; this time, I used a cheap Harbor Freight rolling bender with modifications from the 4×4 Forums that provide “weld on” wings, and the ability to make it motorized with a Harbor Freight pipe threading machine. I couldn’t roll the complete circle with it attached to my stand below:


(the picture shows it fully rolled, but it was AFTER I and moved it). The problem is my tubing would hit the top of my carport before I could make a complete circle. So, I rolled it mainly on the side, and made the Harbor Freight pipe threader have an on/off switch. This was more of a necessity rather than an innovation, as the switch on the thing failed. I quickly realized it was much easier to operate without me holding the switch on and it was quite handy to have an on/off switch instead of a button.

General parts list:

Arduino Micro Pro
Analog LED strips (ie: one color at a time, NOT individually addressable because I didn’t have enough memory in the Micro to do it)
N-channel MOSFETs
1 1/2″ OD aluminum tubing (with 1/8″ sidewall)
Steel tubing for inserts that fits the inner diameter (1 1/4″ OD, but I turn it on the lathe to make it fit better)
PVC tubing
High temp clear hot glue gun glue
Strong packing tape
8 1.2v rechargeable batteries

The controller is an Arduino Micro Pro. It is small enough to fit in the wheel. I wired it up as recommend by Adafruit’s LED strip guide which is to use an N-channel MOSFET (from Fry’s electronics) as seen here:


The battery pack is made up of 8 AA cells. Each cell 2-pack AA battery pack holders from Fry’s (Radio Shack also has them, and you can buy them online). I wired the pack up in series to create about 9.6v total; a little low than the recommend 12 volts to drive the LED strips, but it worked fine. If you use non rechargeable batteries they are at a slightly higher voltage, and will give you 12v out.


Each section of the 5 piece wheel is independent and can be taken apart. I soldered into the LED strips for each wire (one for each color, red/green/blue and a 12v source), and drilled a small hole close by them. The hole is past where the insert comes up to; however, if I were to do it again, I’d put the hole further away from the insert, as the wires inside sometimes bunch up. The wires go inside the wheel (through a grommet) and out the end:


In the picture above, the LED strip is way too close to the insert holes. I originally was going to run two strips; one on each side of the holes, and slightly off the inner diameter so I wouldn’t apply too much pressure on them. I didn’t do this because of time (and cost), and wanted to see if the LEDs could survive with my weight (the answer is no…many are loosing a few colors when connections break due to my weight on them). When I put the wheel together I initially had a short; it was because the metal screw grounded the LEDs right not he above insert hole. I had to pull the LEDs off and move them over a bit to get it to work.

Once out the end, I installed connectors. These connectors suck and I just got them from Frys…instead, I wish I would have had time to get some good ones from the internet (two are also silly; only one is needed but it is what I could find on short notice). The wire lengths are long enough to go past the insert on one side, and on the other piece that mates to it they are short; this is so you can take one side of the insert off and disconnect it easily, without having excess wire (which would be hard to push into the wheel).


Here’s the battery detail; in this picture it has a fuse..but the fuse was too big and I had to remove it. The arduino is stuffed into the side on the left, and the battery fits on the side on the right. It just slips into the wheel and there is a “stop” that prevents it from going into the wheel too far. The stop is just a screw drilled and tapped (you can see it on the wheel, adjacent to the second battery from the right):


The insert can be used to push the battery pack inside the wheel. The pack is removed by pulling on the wire; the cells can be removed and recharged.

The arduino is stuffed into the left side of the wheel; it is held in by friction and nothing more. I can pull it out (gently) by using the wires…it is sort of tough to get out, so I embedded a metal wire inside to help me get it in and out. If I were to do its gain, I’d make the wiring sleeker so it slips in more easily.

The inserts are steel tubing; I think I used 3/16″ thick tubing, and turned it on the lathe to fit inside the wheel (like normal). For the 1.5″ outer diameter aluminum tubing, I think I turned the outer diameter of the inside steel tubes to 1.228″ (they should be 1.250″ if they fit perfect…but they need some slop to slide in without trouble). 1.235″ was too big still.

That’s the basics. I have videos detailing it that I’ll post too.

Things I didn’t post: the tubing was cut and re-glued together with a hot glue gun and high temp clear hot glue. I then put packing tape over it to make it smoother. It works “okay”, but they come apart over time — especially after a week at burning man. I’d like to find some material that is better at gluing the PVC tubing together, or gluing it to the metal wheel.

As I mentioned before, some LEDs are dying. My weight on them makes them loose a connection and they don’t do the full color spectrum. I need to figure out how to solve that. Another problem is that if the wheel is dropped or hits the ground hard, it will black out; I have a bad connection somewhere, and rebooting is pretty slow (I need to remove the Arduino boot loader to make it boot faster)..

Coffee Cup Stirling Engine

Over winter break I started on a project I’ve been wanting to do for a long time. A coffee cup stirling engine, made from scratch based on plans from Jan Ridders.


It “almost works”. The bearings seem to be too big, and the shaft has a lot of slop. I had machined the shaft to the side I thought the bearings were going to be (3mm), but they are larger! I need to remake that part and see if it works.

Some work in progress shots. Power piston (graphite), cylinder (brass), crank shaft (steel), flywheel (alum), stand (alum in brass).


Several tries to get these right:


Flycutting stuff and testing the displacer fit in the groove.


Making the flywheel:


Corbin V-36

I’m working on a V-Frame 36’er unicycle, called the “Corbin V-36“.

It’s partially an experiment to see how light I can make it, yet still be strong and not flex.

I did a 3d model in Sketchup, and printed it full size. I then machined a jig to hold things in place. Here’s a video explaining the jig:

And some pictures. The jig setup for my my main seat post tube:


Experimenting with bending:


I’m using cro-moly tubing, 1/2″ OD by .049 wall thickness. It is too small of tubing, and the frame flexes when going up hills. I’m going to use 7/8″ tubing next, and try to re-enforce this frame.

Working the corners in my jig:



Jig and frame almost setup to weld the front post tube:


Clamped together, and brazing started:


Popped out of the jig and a test fit:


Setting up the main seat post:


After it was brazed on:


Horizontal support, bent to match the tire diameter, brazed on, and a test handlebar tossed on:


The frame flexes *a lot* going uphill. I have to use larger tubing for the seat post to fix that. I brazed on some lower supports to try to prevent flex, but it didn’t help much. I’m going to braze on another tube really close to my seat post to try to get this frame to work. Then, if it does, I’ll make another one with thicker tubing.

Due to heat distortion, I had to ream out both tube holes to get the stuff to go into them.

Plug Bug: Broken brake…

…well, problems come in pairs. I changed my front brake pads about about 8600 miles; they wore away quickly! I didn’t change the rear, as they weren’t as bad as the front. I checked the new front ones at 15,000 miles and they are doing great. I had looked at the rear but only on one side and without taking the wheel off. They looked okay, so I wasn’t going to do them yet. However, the rear brakes started making a horrible noise last Friday.

So today I decided to take the brakes apart and drop in the new pads I already had on hand. It turned out to be an all day adventure. The left pads were worn, and it was time to replace them, but they weren’t totally shot. The right rear wasn’t in such good shape. Of the two pads, the left pad wore twice as fast, and was starting to etch into the disc! Doh! It wasn’t that bad, and I’m not going to replace the disc, but I had some trouble with installing the new pads. First of all, the pistons on the calipers were not wanting to go back in. I had to force them in with a pretty large C-clamp, and even then it was a lot of effort to get them in. Then I encountered the “problem”.

I have the rear disc brake conversion kit from CIP1. It is this one. It turns out one of the bolts that moves in and out to let the brake adjust was seized. So instead of moving as the pads wore, it just stayed put, and caused one side of the pad to wear twice as fast as the other! Worse, it was impossible to get off. I tried lots of things, including heating it with the torch, but it wasn’t budging. I put a bolt in and tried to get it to move…but that was a bad idea as the bolt snapped right off! That made things worse. I took the piece off the car and worked it in my vice and finally got it out.

In the picture below, the bottom right hole is where it was stuck; I managed to get it out by working it in a vice for a while.


The stuck piece freed:


Apparently some water got in the hole and let things rust up nice and bad. The sucky part is that I broke the bolt off in the piece:


..and easy outs (bolt extractors) *never* work for me. So, I of course broke one off in it.

I wasn’t sure what to do. I could order a new caliper (i.e.: this one). for $120 plus shipping, and wait a week to get it…but I don’t want to do that as it means week of not driving and I also have a car show to go to next Saturday! Instead, I decided to machine my own piece. So, after some time on the lathe and mill I had a replacement.

In the picture below, the top is the broken piece, the middle is the good piece+bolt, and the bottom is what I made. After the picture was taken, I quenched it in oil to harden it (note to self: don’t do it in a plastic container).


The finished piece is on the right, and the material I used is the big lump of steel.


My short test drive seems to let the brakes work! Cool…it only took all day (~10am to 8pm). And I missed hanging out with my friend Nathan for his birthday! Doh…

Roue Cyr: Making a wheel – skinning

I’m doing a series of videos on how I made my second Roue Cyr (Cyr Wheel — aka: Simple Wheel).

Here’s the last in the series…which is skinning.

Updated notes: Use pipe clamps to secure the air attachment on! Heat it in the oven for ~3 minutes. Spray water on it from a bottle if it has trouble going over. If this method doesn’t work, the alternative is to skin the wheel while it is hot bath water, and then let it dry out for a few days before assembling.

How to skin a roue cyr wheel

Email me if you have questions.

New pull up bar

Using the plasma cutter to make stuff…

I wanted a new pull-up bar for my house. The old one looked tacky…but how can anything be tacky around your own house if you put it there? Here’s some shapes cut out of metal:


Pieces setup for welding:


Ugly pullup bar removed:


Hanging on the wheel (as seen through the eyes of a lyra. And in this picture you can see how the top right of the lyra wasn’t quite as circular as I wanted…)


Cube Hanger

I needed somewhere better t hang my cube when I wasn’t using it. So, I made a cube hanger!

I used the plasma cutter to cut some pieces of 3/16’ish steel plate (from the scrap yard):


Cut out:


I TIG welded on some 1.5″ pipe at a 45 angle:


Cleaned it up, and powder coated it flat black:


Bolted it to my beam (it is super strong!):


And hang the cube! It is a little close to the wall, but out of the way. It is kind of fun to sit in it, so I’ll probably whip up another one more in the center of the room to hang for parties and stuff.


Metal Coat Rack

What a better use for an old VW brake drum?





A few in progress shots:


Initial sketch and idea:


Plasma Cutter

I got a new tool a few weeks ago. A plasma cutter!


After doing some research, I went with a Thermal Dynamics Cutmaster 52. It is awesome!


I also had to get a new air compressor to keep up with it. I went with a Husky one from Home Depot; it has a three year warranty, whereas most other ones of the same size have a 1 year warranty. Plus, there were lots of good reviews on


(c) 2008-2017 Corbin Dunn

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